US2102107A - Production of ammonium sulphate - Google Patents

Description

, f fuNiTED STATES PATENT 1F Patented Dec. 14, 71937- Y l2,102,107 v .o PRODUCTION oF AmioNIUM SULPHATE Drawing. Application March 3, 1934, Serial No. 713,882. In the Netherlands October 16,

10 Claims. (C1`. 234119) o My invention relates. to the production of ammonium sulphate and hasV for one of its objects to provide .means Vwhereby a particularly coarsegrained ammonium sulphate is obtained.

The invention is more particularly concerned with the production'of an `ammonium sulphate of4 thischaracter byeway of saturation or neutralization of commercial sulphuric acidjsuch as is obtained inthe vitriol chamber process. I-Iitherto,` in order to obtain ammonium sulphate in large crystals, it has been tried toin- Iluence theV formation of: thissalt `by mechanical meanssuch-aswagitationy forcing of the gaseous ammonia into the saturation liquor (acid) mixingoix-the ammonia with inert gases, etc. Thus the specicationfof French Patent 663,105 recommends diluting the ammonia gas with'steam, air,` some other inert gas or a mixture of such gases vor vapors. However besides 'the physical conditions, under which `the compound' is being formed; also the chemical conditions must bel taken linto 'account, such asforinstancethe degreeV of acidity ofthe saturation liquor, which has been shown tobe particularly important. As is well known, this aci'dityshoi'ild be keptlasV low as possible. Apart therefrom it is a well known factf'that in allprocesses based on crystallization'the presence 'of foreign matter, such as the impurities brought in by the reacting compounds, often playsan important role, since all solidsY present in the liquor` may considerably iniluene the growth 'of the crystals in certainA directions. Whenever the commercial sulphuric acid contained-considerable quantities oi impurities, which accumulate in the `saturation liosu'or7 careful attention has been paid Ato,` theiniluenoe'which these impurities exertedion the crystallization 'and ,one has tried toy avoid or at least `reduce the uniavorable actionby adding chemical reagents, l f In claim 2 of French Patent 663,105` mentioned above this principle issetout in ageneral manner as followsi- Y n .To the diluted or'undiluted ammonia Vgas or to the diluents orto the saturation liquor itself lchemical,agents are added either Vin gaseous or in liquid form for the purpose of changing the appearance and` hardness of the kcrystals of ammoniumsulphataeither by direct action on. the sulphate or by acting on the impurities present in theliquor or inthediluentfv i Injlines .4'7 to 51, page 2, the French specica.- 4tion further states thatA by combining thertwo steps the form, volume, hardness Vand color of the ammonium sulphate can be regulated` as desired.

The present invention contemplates changing the character of the crystals of ammonium` sulphateV in accordance with the teachings ofthe French specification by adding to the, saturation liquor a phosphatic compound such as phosphoric acid or a phosphate. lI have found that theslight change thus brought about in the cornposition of the saturation liquor suices, ifl the general physical conditions of operation are favorable, to obtain a coarse-grained ammonium sulphate. i

I prefer adding to the saturation liquor, while it still contains free acid, either asmall quantity of phosphoric acid or a phosphate soluble in water or in dilute acid. I may however alsofadd a raw'phosphate, which has either been decomposed before being added or is introduced-f as such into the saturation liquor to be decomposed ktherein by theacid forming part of'this liquor. y Y

The quantity of phosphoricY acid or phosphate addedcan be nicely adjusted, taking-into 'account the introduction of impurities by-'the'sulphuric acid or by other agents -introducedinto the saturation vessel. Whenthe phosphate-"is added tothe. saturation liquor, a small quantity of a precipitate will form. Ii may now for' instance add a quantity of phosphate such that onfafurther quantity of-'phos'phate being added,

no further precipitate is formed. In accordance with the character of the final product tobe obtained Imay however also add-only so much phosphate,that Vonly part of the impurities pre- .cipitatable by phosphate are removed.

`-The constitution of the' precipitate varies 'in accordance with the character vof the'impurities present.' Thusfif impure sulphuric'acid is used, all ferrie ions present thereinV vwill be precipitated by the phosphate under the form of ferrie phosphate.AV The same applies to the aluminium which is also present in impure sulphuric acid. -If chromium should be present7 this metal will also be found in the phosphate precipitate. The analytical chemist knows that all these precipitates are formed only in -a neutral or ina very slightly acid medium. ItI is therefore particularly surprising to see that such precipitates will also form at elevated temperature in a saturation liquor containing free sulphuric acid. I operate with a liquor containing not more than 1.5% free acid, calculated as'sulphuric acid.

The crystals Vof ammonium sulphate are removed, ifv desired together with the phosphate precipitate, from the saturation vessel and subjected to further treatment as usual.

In order to illustrate the advance obtained by the addition of phosphoric acid or a phosphate to the saturation liquor. I will rst describe the production of ammonium sulphate as hitherto practised, i. e. without the addition of phosphoric acid or a phosphate.

According to the old mode of proceeding a mixture of ammonia gas, obtained by synthesis, with air and steam is introduced in a saturation vessel containing 13 cubic metres of a saturation liquor saturated with ammonium sulphate, having a temperature of about 108 C., a ferric ion content of 2 grams per litre and a content of 6% free H2SO4, the degree of acidity of the liquor being kept constant by the equivalent addition of commercial sulphuric acid of 58 to 60 B. containing .5 gram ferric ion per litre. The addition of ammonia gas and sulphuric acid is regulated in such manner, that 75 tons ammonium sulphate are produced 'within 24 hours. The ammonium sulphate formed in the reaction is continuously removed from the vessel and after centrifuging and drying a product is obtained, in which the crystals present a proportion of length to width of about 10:1. On this product being sifted, 25% of the crystals will be found to bc larger than .5 mm., while 71.5% are larger than .2 mm. In view of the presence of ferric ions and arsenic the degree of acidity of the saturation liquor cannot be reduced, since otherwise colloidal compounds of iron and arsenic will separate out, which tend to disturb the process.

In contradistinction thereto, if, in accordance with the present invention, 20 kgs. oi a 14% superphosphate are added per hour to the saturation liquor constituted as described above, but the degree of acidity of which is reduced to .5 to 1% free H2SO4, the ferric ion content of the mother liquor will drop to about .04 gram per litre, and while all other physical and chemical conditions of operation including the composition of the acid introduced and the quantity of ammonium sulphate produced remain the same. I obtain a product, the crystals of which present an average proportion of length to width of 1.521. On this product being sifted it will be found that '77.5% of the crystals are larger than .5 mm. and 98% larger than .2 mm. I'he product does not dust, is excellently suited for strewing and shows almost no tendency to cake.

Instead of the 20 kgs. of a 14% superphosphate I may also add hourly for instance 7 kgs. of a 40% superphosphate, or 5.6 kgs. diammonium phosphate (NH4)2IIPO4 or 4.6 kgs. monoammonium phosphate NH4II2PO4 or 4.2 kgs. phosphoric acid H3PO4 of 66% or 'l kgs. dicalcium phosphate CaHPO4.2I-I2O of 41% or 11.2 kgs. of raw calcium phosphate CasPOi of 25%.

These additions may be introduced either into the saturation liquor or into the sulphuric acid to be added to it. More especially when using raw phosphates I prefer adding them to the acid direct.

Various changes may be made in the details disclosed in the foregoing specication without departing from the invention or sacricing the advantages thereof.

I claim:-

1. In the preparation, by the saturation process, of ammonium sulphate in relatively coarse crystalline form from solutions prepared with commercial sulphuric acid containing the usual small amounts of metallic impurities, the process which comprises adding to such a solution, while maintaining the concentration of sulphuric acid therein below 1.5 per cent, a soluble phosphatic compound in amount not substantially more than sufficient to precipitate said impurities from solution thereby producing a liquor having a reduced content oi said metallic impurities in dissolved form, crystallizing ammonium sulphate from said liquor and recovering the coarse crystals thereby produced.

2. The process of claim 1 wherein the concen tration of the sulphuric acid in said liquor is maintained between about 0.5 and 1.5 per cent.

3. The process of claim 1 wherein the soluble phosphatic compound is phosphoric acid.

4. The process of claim 1 wherein the soluble phosphatic compound is superphosphate.

5. 'I'he process of claim 1 wherein the soluble phosphatic compound is a raw phosphate.

6. The process of claim 1 wherein sulphuric acid is added to said liquor to maintain a concentration below 1.5 per cent and wherein said phosphatic compound is added to the sulphuric acid prior to its introduction into said liquor.

'7. In the preparation of ammonium sulphate in. relatively coarse crystalline form from commercial sulphuric acid solutions containing the usual small amounts of metallic impurities, the process which comprises adding to such a solution, while maintaining the concentration of sulphuric acid therein below 1.5 per cent, a soluble phosphatic compound in amount not substantially more than suiiicient to precipitate said impurities from solution thereby producing a liquor having a reduced content of said metallic impurities in dissolved form, adding ammonia to said solution, crystallizing ammonium sulphate from said liquor and recovering the coarse crystals thereby produced.

8. In a continuous saturation process for producing ammonium sulphate from ammonia gas and commercial sulphuric acid containing dissolved metallic compounds which tend to accumulate in the saturation liquor, the steps whichconsist in maintaining the saturation liquor at an acidity of not more than 1.5% figured as H2SO4, supplying to the saturation liquor a soluble phosphatic compound in amount not substantially more than suiiicient to react with said metallic compounds to convert them into insoluble phosphates, allowing crystallization of the ammonium sulphate to proceed until coarse grained crystals are produced. and then removing said coarse grained crystals with any accom panying insoluble metallic phosphates.

9. In a continuous saturation process for producing ammonium sulphate from cyanogen-free ammonia gas and commercial sulphuric acid containing dissolved metallic compounds which tend to accumulate in the saturation liquor, the steps which consist in maintaining the saturation liquor at an acidity of not more than 1.5% lgured as H2SO4, supplying to the saturation liquor a soluble phosphatic compound in amount not substantially more than suflicient to convert said metallic compounds to insoluble phosphates, allowing crystallization of the ammonium sulphate to proceed until coarse grained crystals are produced, and then removing said coarse grained crystals with any accompanying insoluble metallic phosphates.

10. In a continuous saturation process of producing ammonium sulphate from ammonia and commercial sulphuric acid containing dissolved iron compounds which develop ferric ions tending to accumulate in the saturation liquor, the steps which comprise maintaining the saturation liquor at an acidity of not more than 1.5%, calculated as H2504, supplying to the saturation compounds which are insoluble in the saturation liquor, allowing crystallization of the ammonium sulphate Ato take place, and removing from the saturation liquor crystals of ammonium sulphate and any insoluble phosphatic iron compounds 5 which accompany said crystals.

GERRAIT BERKHOFF. J n.